Two concurrent pathways of the reaction of pyrrolobenzoxazinetriones with cyclic alkoxyolefins. Synthesis of alkaloid-like pentacyclic 6/6/5/6/5- and 6/6/5/6/6-angularly fused heterocycles

Article abstract of DOI:10.1134/S1070428017010134

3-Aroylpyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones reacted with 2,3-dihydrofuran and 3,4-dihydro-2H-pyran to give mixtures of the corresponding hetero-Diels–Alder and Michael addition products.

Full text of DOI:10.1134/S1070428017010134

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2017, Vol. 53, No. 1, pp. 74–81. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © E.E. Stepanova, M.V. Dmitriev, P.A. Slepukhin, A.N. Maslivets, 2017, published in Zhurnal Organicheskoi Khimii, 2017, Vol. 53,
No. 1, pp. 78–85.
Two Concurrent Pathways of the Reaction
of Pyrrolobenzoxazinetriones with Cyclic Alkoxyolefins.
Synthesis of Alkaloid-Like Pentacyclic 6/6/5/6/5-
and 6/6/5/6/6-Angularly Fused Heterocycles
E. E. Stepanovaa, M. V. Dmitrieva, P. A. Slepukhinb, and A. N. Maslivetsa*
a Perm State National Research University, ul. Bukireva 15, Perm, 614990 Russia
*e-mail: koh2@psu.ru
b Postovskii Institute of Organic Synthesis, Ural Branch, Russian Academy of Sciences,
ul. S. Kovalevskoi/Akademicheskaya 22/20, Yekaterinburg, 620990 Russia
Received July 14, 2016
Abstract—3-Aroylpyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones reacted with 2,3-dihydrofuran and 3,4-dihy-
dro-2H-pyran to give mixtures of the corresponding hetero-Diels–Alder and Michael addition products.
DOI: 10.1134/S1070428017010134
A combination of high stereoselectivity, atom
economy, and experimental simplicity makes hetero-
Diels–Alder reactions a valuable synthetic approach to
polyheterocyclic compounds [1–3]. It was shown pre-
viously that monocyclic 4-acyl-1H-pyrrole-2,3-diones
act as heterodienes in [4+2]-cycloadditions to cyclic
and acyclic alkoxyolefins to afford substituted pyrano-
[4,3-b]pyrroles with high diastereoselectivity (only
endo-cycloadducts were obtained) [4–10].
pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones with
cyclic alkoxyolefins.
The reactions of aroylpyrrolobenzoxazinetriones
1a–1f with 2,3-dihydrofuran (2a) and 3,4-dihydro-2H-
pyran (2b) were carried out at a reactant ratio of 1:1.5
in benzene under reflux until disappearance of the
violet color typical of compounds 1a–1f (2–90 min).
As a result, mixtures of Michael adducts 3a–3j and
cycloadducts 4a–4j were formed, which were separat-
ed by fractional crystallization [15] (Scheme 1).
4-Acyl-substituted 1H-pyrrole-2,3-diones fused
through the N1–C5 bond to a benzo[b][1,4]oxazin-2-
one fragment (3-aroylpyrrolo[2,1-c][1,4]benzoxazine-
1,2,4-triones) are interesting model structures for
studying hetero-Diels–Alder reactions due to the pres-
ence in their molecules of a nonplanar heterodiene
fragment (C3a=C3–C=O), which hinders cycloaddition
according to the concerted mechanism or makes it
impossible. The cycloadditions of 3-aroylpyrrolo-
[2,1-c][1,4]benzoxazine-1,2,4-triones and their aza
analogs, 3-aroylpyrrolo[1,2-a]quinoxaline-1,2,4(5H)-
triones and 3-aroyl-4-arylpyrrolo[1,2-a]quinoxaline-
1,2-diones, with acyclic alkoxyolefins lead to the
formation of mixtures of diastereoisomeric [4 +2]-
cycloadducts, the exo adducts being the major products
[11–14]. In order to find out how the dienophile struc-
ture affects the direction and diastereoselectivity of the
above cycloadditions, we studied reactions of 3-aroyl-
Compounds 3a–3j are high-melting (with decom-
position) yellow crystalline substances that are readily
soluble in DMSO, aromatic and halogenated hydro-
carbons, ethyl acetate, acetone, 1,4-dioxane, and alco-
hols, poorly soluble in carbon tetrachloride and
saturated hydrocarbons, and insoluble in water. They
showed a positive color test (cherry color) for enolic
hydroxyl on treatment with an alcoholic solution of
iron(III) chloride.
The IR spectra of 3a–3j (mineral oil) contained
absorption bands due to stretching vibrations of the
hydroxy group (3087–3200 cm–1) and lactone (C4=O,
1766–1785 cm–1), lactam (C1=O, 1690–1727 cm–1),
and ketone carbonyl groups (3-C=O, 1641–1664 cm–1).
1
Compounds 3a and 3e–3j showed in the H NMR
spectra (DMSO-d6) signals from protons of the methy-
lene groups, aromatic rings and substituents therein,
74

TWO CONCURRENT PATHWAYS OF THE REACTION OF PYRROLOBENZOXAZINE...
75
Scheme 1.
O
O
O
Y
O
C(O)Ar
R
N
a
O
N
O
O
O
N
O
O
Y
O–
O
O
O
Y
OH
3a–3j
+
R
R
Ar
Ar
H
O
O
Y
O
O
H
O
O
Ar
1a–1f
2a, 2b
A
R
N
b
O
OH
4a–4j
1, R = H, Ar = Ph (a), 4-EtOC6H4 (c), 4-BrC6H4 (d), 4-MeOC6H4 (e), 4-O2NC6H4 (f); R = Cl, Ar = Ph (b); 2, Y = CH2 (a), CH2CH2 (b);
3, 4, Y = CH2, Ar = Ph, R = H (a), Cl (b); R = H, Ar = 4-EtOC6H4 (c), 4-BrC6H4 (d); Y = CH2CH2, Ar = Ph, R = H (e), Cl (f); R = H,
Ar = 4-MeOC6H4 (g), 4-EtOC6H4 (h), 4-BrC6H4 (i), 4-O2NC6H4 (j).
a signal from the vinylic proton in the furan or pyran
ring [multiplet (3a) or singlet (3e–3j)] in the region
δ 6.23–6.46 ppm, and a broadened singlet from the
enolic hydroxy group at δ 11.54–11.93 ppm. In the
1H NMR spectra of 3b–3d recorded from solutions in
CDCl3, the vinylic proton signal appeared as a multi-
plet in the region δ 6.30–6.35 ppm, and the OH signal
was a broadened singlet at δ 9.34–9.87 ppm.
The 13C NMR spectra of 3a–3e and 3g–3i in
DMSO-d6 or CDCl3 displayed signals at δC 67.4–71.1
(C3a), 106.4–109.3 (C4′ in 3a–3d or C5′ in 3e and 3g–
3i), 113.1–116.9 (C3), 141.8–143.3 (C5′ in 3a–3d or C6′
in 3e and 3g–3i), 148.0–153.3 (C2), 160.9–163.1 (C4),
162.4–164.3 (C1), and 187.6–190.2 ppm (3-C=O).
43.6 (C2), 58.8–59.3 (C1), 68.6–69.3 (C4), 96.7–99.4
(C6), 103.1–104.1 (C9), 159.2–159.9 (C11), 162.0–
163.1 (C20=O), 167.0–170.4 (C8), 173.9–176.1 (C10).
In the 13C NMR spectra of 4e–4i in DMSO-d6, the
corresponding signals were located at δC 32.5–33.9
(C2), 60.6–61.0 (C1), 60.8–61.7 (C5), 96.9–97.6 (C7),
97.8–99.4 (C10), 160.0–160.6 (C12), 162.9–166.1 (C21),
165.7–167.4 ppm (C9), and 175.5–176.2 ppm (C11).
Also, signals of the methylene carbon atoms and
aromatic substituents were present in the spectra of
4a–4c and 4e–4i.
According to the X-ray diffraction data (Fig. 1),
compound 3i crystallized in space group Ia–3d belong-
ing to the cubic crystal system, which is very rare for
organic compounds. The bond lengths and bond angles
Compounds 4a–4j are yellow crystalline substances
melting with decomposition at high temperature. They
are poorly soluble in DMSO, aromatic and halogenated
hydrocarbons, ethyl acetate, acetone, and 1,4-dioxane,
and insoluble in alkanes and water.
O6
C14
C15
C16
C17
C13
C5
C12
O4
O5
O2
C6
The IR spectra of 4a–4j dispersed in mineral oil
displayed absorption bands at 1766–1793 (lactone car-
bonyl) and 1710–1741 cm–1 (lactam and ketone car-
bonyls). In the 1H NMR spectra of 4a–4d in DMSO-d6
or CDCl3 we observed signals from methylene groups
and aromatic rings and substituents in the latter,
a multiplet at δ 3.02–3.22 ppm due to 2-H, and a dou-
blet at δ 6.00–6.05 ppm (J = 5.3 Hz) due to 6-H. The
2-H and 7-H protons of 4e–4j resonated in the
1H NMR spectra (DMSO-d6) at δ 2.44–2.60 (m) and
5.71–5.80 ppm (d, J = 3.5–4.0 Hz), respectively.
C11
C4
C10
C1
N1
C3
C23
C9
C8
C18
C2
C22
C19
C7
C20
Br1
O3
O1
C21
Fig. 1. Structure of the molecule of 3-(4-bromobenzoyl)-3a-
(3,4-dihydro-2H-pyran-5-yl)-2-hydroxypyrrolo[2,1-c][1,4]-
benzoxazine-1,4(3aH)-dione (3i) according to the X-ray dif-
fraction data.
The 13C NMR spectra of 4a–4c in DMSO-d6 or
CDCl3 contained the following signals, δC, ppm: 42.2–
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 53 No. 1 2017

STEPANOVA et al.
bonds which link them to three-dimensional tetramers,
76
and the latter give rise eventually to a non-primitive
cubic unit cell. The atoms involved in intermolecular
hydrogen bonding form fairly wide pores oriented
along one of the fourth-order symmetry axes (Fig. 2).
Compound 4f (Fig. 3) crystallized in P-1 centro-
symmetric space group belonging to the triclinic crys-
tal system. All bond lengths and bond angles in
molecule 4f fall within the corresponding reference
ranges. The pyrrole ring is planar, the tetrahydropyran
ring appears in a chair conformation, and the dihydro-
pyran and oxazine rings adopt a distorted sofa con-
formation bent through dihedral angles of 41.2 and
49.4° along the C19C8 and C7N1 lines, respectively. The
crystal packing of 4f is stabilized by van der Waals
interactions without essential contribution of specific
short contacts.
Compounds 3a–3j were isolated as the major prod-
ucts, while 4a–4j were the minor ones. The ratio 3/4
depended on the solvent used. When the reaction was
carried out in benzene, the ratio 3/4 was ~2:1 (accord-
Fig. 2. A fragment of crystal packing of 3-(4-bromobenzoyl)-
3a-(3,4-dihydro-2H-pyran-5-yl)-2-hydroxypyrrolo[2,1-c]-
[1,4]benzoxazine-1,4(3aH)-dione (3i).
1
ing to the H NMR data for reaction mixtures),
whereas in 1,4-dioxane and acetonitrile the product
ratio was ~2:1 and ~10:1, respectively. Furthermore,
the violet color of compounds 1a–1f in the reaction
carrier out in acetonitrile disappeared more rapidly
than in benzene.
in molecule 3i are close to the corresponding reference
values, except for some deviations related, in partic-
ular, to the presence of sp3-hybridized C10 atom among
bridgehead carbon atoms of the conjugated tricyclic
system. The enolic proton in the O2C17C9C8O3 frag-
ment is located on the O3 atom of the dihydropyrrole
ring, and this structure is stabilized by strong intramo-
lecular hydrogen bond with the O1 atom of the neigh-
boring carbonyl group. The 3-oxacyclohexene ring
adopts a sofa conformation with strong thermal dis-
ordering of the C14 atom. Molecules 3i in crystal are
packed through a system of intermolecular hydrogen
Hetareno[e]pyrrole-2,3-diones 1a–1f reacted with
2,3-dihydrofuran (2a) appreciably more readily than
with 3,4-dihydro-2H-pyran 2b, which is very consis-
tent with the Mayr–Patz nucleophilicity scale [16, 17].
We previously believed [15, 18] that compounds
3a–3j are formed as a result of either nucleophilic
addition of cyclic alkoxyolefins 2a and 2b to hetareno-
[e]pyrrole-2,3-diones 1a–1f or hydrolysis of diastereo-
isomeric compounds 4a–4j with subsequent dehydra-
tion or isomerization of 4a–4j. However, no signals
assignable to diastereoisomers of 4a–4j were observed
O2
C23
O1
O5
C19
O6
C3
C7
C20
C4
C2
C22
1
in the H NMR spectra of the reaction mixtures. The
C21
C8
N1
C12
C18
corresponding compounds 3a–3j and 4a–4j were not
converted into each other on heating in organic sol-
vents (benzene, 1,4-dioxane, acetonitrile) under reflux
or on melting (TLC, UHPLC). Hydrolysis of 4a–4j on
heating in organic solvents (benzene, 1,4-dioxane,
acetonitrile, DMSO) in the presence of water, as well
as of acid catalysts (acetic acid or HCl) or by keeping
these compounds in the same media at room tempera-
ture for several weeks did not produce compounds 3a–
3j (TLC, UHPLC). These findings indicated that the
most probable way of formation of compounds 3a–3j
C5
C1
Cl1
C13
C17
C11
C6
C14
C10
C9
C16
C15
O3
O4
Fig. 3. Structure of the molecule of (2S*,1R*,7R*)-16-
chloro-9-phenyl-6,8,20-trioxa-13-azapentacyclo-
[11.8.0.01,10.02,7.014,19]henicosa-9,14,16,18-tetraene-11,12,21-
trione (4f) according to the X-ray diffraction data. Hydrogen
atoms are not shown for clarity.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 53 No. 1 2017

TWO CONCURRENT PATHWAYS OF THE REACTION OF PYRROLOBENZOXAZINE...
77
and 4a–4j is nucleophilic addition of cyclic alkoxy-
olefins 2a and 2b to the C3a atom of hetareno[e]pyr-
role-2,3-diones 1a–1f to give zwitterionic intermediate
A (Scheme 1). The latter undergoes either 1,5-proto-
tropic shift leading to adducts 3a–3j (pathway a) or
intramolecular cyclization involving the cationic
carbon atom of the cyclic alkoxyolefin residue and and
carbonyl oxygen atom of the aroyl substituent, yielding
4a–4j (pathway b). Compounds 4a–4j are formed as
a single diastereoisomer (endo cycloadduct) which is
not typical of reactions of hetareno[e]pyrrole-2,3-di-
ones like 1 with olefins [11–14, 19].
(compound 4a) was filtered off. The mother liquor was
diluted with 70 mL of hexane, and the yellow solid
(compound 3a) was filtered off. Yield 0.73 g (60%),
mp 262–263°C (decomp., from hexane). IR spectrum,
ν, cm–1: 3200 br (O–H), 1766 (C4=O), 1697 (C1=O),
1
1651 (3-C=O). H NMR spectrum (400 MHz,
DMSO-d6), δ, ppm: 2.34 m and 2.51 m (1H each,
3′-H), 4.16 m and 4.37 m (1H each, 2′-H), 6.38 m (1H,
5′-H), 7.33–7.92 m (9H, Harom), 11.74 br.s (1H, OH).
13C NMR spectrum (100 MHz, DMSO-d6), δC, ppm:
27.5 (C3′), 63.3 (C2′), 70.2 (C3a), 109.3 (C4′), 114.9
(C3), 116.4–137.6 (Carom), 143.3 (C6′), 145.6 (Carom),
150.2 (C2), 160.9 (C4), 162.4 (C1), 189.9 (3-C=O).
Found, %: C 67.75; H 3.93; N 3.68. C22H15NO6. Cal-
culated, %: C 67.86; H 3.88; N 3.60.
Molecules 4a–4j possess a pentacyclic alkaloid-like
skeleton based on perhydrobenzo[c]indene structure.
Interest in compounds containing such structural frag-
ment continuously increases since many structurally
related natural compounds (dankasterone [20], preta-
zettine [21], erythroidine [22, 23], etc.) possess
pronounced biological activity.
Compounds 3b–3j and 4b–4j were synthesized
in a similar way.
3-Benzoyl-8-chloro-3a-(2,3-dihydrofuran-4-yl)-
2-hydroxypyrrolo[2,1-c][1,4]benzoxazine-1,4(3aH)-
dione (3b). Yield 0.77 g (58%), mp 243–244°C
(decomp., from hexane). IR spectrum, ν, cm–1: 3188 br
(O–H), 1783 (C4=O), 1714 (C1=O), 1650 (3-C=O).
1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 2.31 m
and 2.46 m (1H each, 3′-H), 4.24 m and 4.35 m (1H
each, 2′-H), 6.30 m (1H, 5′-H), 7.29–7.88 m (8H,
Harom), 9.87 br.s (1H, OH). 13C NMR spectrum
(100 MHz, CDCl3), δC, ppm: 27.6 (C3′), 64.1 (C2′),
71.1 (C3a), 106.9 (C4′), 115.3 (C3), 117.9–136.6 (Carom),
141.8 (C6′), 142.4 (Carom), 148.2 (C2), 161.3 (C4),
162.6 (C1), 189.8 (3-C=O). Found, %: C 62.27;
H 3.49; N 3.35. C22H14ClNO6. Calculated, %: C 62.35;
H 3.33; N 3.31.
EXPERIMENTAL
1
The H and 13C NMR spectra were recorded on
Bruker Avance III 500, Bruker Avance DRX-400,
Bruker Avance DRX-500 equipped with a dual carbon/
proton (CPDUL) cryoprobe, and Bruker Avance III
HD 400 spectrometers using tetramethylsilane or
hexamethyldisiloxane as internal standards. The IR
spectra were recorded on FSM-1201 and Perkin Elmer
Spectrum Two spectrometers. The elemental analyses
were obtained on Perkin Elmer 2400 Series II and
Vario MICRO cube analyzers. The reaction conditions
1
were optimized by H NMR (Bruker Avance III HD
3a-(2,3-Dihydrofuran-4-yl)-3-(4-ethoxybenzoyl)-
2-hydroxypyrrolo[2,1-c][1,4]benzoxazine-1,4-(3aH)-
dione (3c). Yield 0.83 g (62%), mp 238–239°C
(decomp., from CCl4). IR spectrum, ν, cm–1: 3188 br
(O–H), 1782 (C4=O), 1690 (C1=O), 1641 (3-C=O).
1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 1.45 t
(3H, Me, J = 7.0 Hz), 2.31 m and 2.45 m (1H each,
3′-H), 4.12 q (2H, CH2Me, J = 7.0 Hz), 4.20 m and
4.32 m (1H each, 2′-H), 6.35 m (1H, 5′-H), 6.93–
7.93 m (8H, Harom), 9.67 br.s (1H, OH). 13C NMR
spectrum (100 MHz, CDCl3), δC, ppm: 14.6 (Me), 27.7
(C3′), 63.9 (CH2Me), 64.0 (C2′), 71.0 (C3a), 107.4
(C4′), 114.2 (C3), 116.8–133.5 (Carom), 143.3 (C6′),
144.0 (Carom), 148.0 (C2), 161.2 (C4), 163.3 (C1),
164.4 (Carom), 187.6 (3-C=O). Found, %: C 66.58;
H 4.35; N 3.36. C24H19NO7. Calculated, %: C 66.51;
H 4.42; N 3.23.
400) and UHPLC monitoring (Waters ACQUITY
UPLC I-Class; Acquity UPLC BEH C18 column, grain
size 1.7 μm; eluent acetonitrile–water, flow rate
0.6 mL/min; ACQUITY UPLC PDA eλ UV detector;
Xevo TQD detector; positive electrospray ionization;
ion source temperature 150°C; capillary voltage 3500–
4000 V; cone voltage 20–70 V; vaporizer temperature
150–300°C). The purity of the isolated compounds was
checked by TLC on Silufol plates using benzene–ethyl
acetate (5:1) as eluent; development with iodine vapor.
3-Benzoyl-3a-(2,3-dihydrofuran-4-yl)-2-hydroxy-
pyrrolo[2,1-c][1,4]benzoxazine-1,4(3aH)-dione (3a).
A solution of 0.33 g (4.7 mmol) of 2,3-dihydrofuran
(2a) in 5 mL of anhydrous benzene was added to a so-
lution of 1.00 g (3.1 mmol) of compound 1a in 10 mL
of anhydrous benzene, and the mixture was refluxed
for 5 min (until the original violet color disappeared).
The mixture was cooled, and the yellow precipitate
3-(4-Bromobenzoyl)-3a-(2,3-dihydrofuran-4-yl)-
2-hydroxypyrrolo[2,1-c][1,4]benzoxazine-1,4-(3aH)-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 53 No. 1 2017

STEPANOVA et al.
78
dione (3d). Yield 0.79 g (55%), mp 200–201°C
(decomp., from hexane). IR spectrum, ν, cm–1: 3200 br
(O–H), 1780 (C4=O), 1715 (C1=O), 1651 (3-C=O).
1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 2.32 m
and 2.44 m (1H each, 3′-H), 4.22 m and 4.36 m (1H
each, 2′-H), 6.32 m (1H, 5′-H), 7.21–7.76 m (8H,
106.6 (C5′), 113.5 (C3), 115.2–131.9 (Carom), 142.7
(C6′), 143.4 (Carom), 153.0 (C2), 161.4 (C4), 162.8 (C1),
163.2 (Carom), 188.4 (3-C=O). Found, %: C 66.68;
H 4.38; N 3.52. C24H19NO7. Calculated, %: C 66.51;
H 4.42; N 3.23.
3a-(3,4-Dihydro-2H-pyran-5-yl)-3-(4-ethoxyben-
zoyl)-2-hydroxypyrrolo[2,1-c][1,4]benzoxazine-
1,4(3aH)-dione (3h). Yield 0.94 g (68%), mp 119–
121°C (decomp., from isooctane). IR spectrum, ν,
cm–1: 3200 (O–H), 1774 (C4=O), 1723 (C1=O), 1654
(3-C=O). 1H NMR spectrum (400 MHz, DMSO-d6), δ,
ppm: 1.36 t (3H, Me, J = 6.9 Hz), 1.59 m (2H, 3′-H),
1.81 m (2H, 4′-H), 3.69 m and 3.87 m (1H each, 2′-H),
4.14 q (2H, CH2Me, J = 6.9 Hz), 6.23 s (1H, 6′-H),
7.00–7.87 m (8H, Harom), 11.54 br.s (1H, OH).
13C NMR spectrum (126 MHz, DMSO-d6), δC, ppm:
14.5 (Me), 17.1 (C4′), 20.9 (C3′), 63.5 (C2′), 65.1
(CH2Me), 67.5 (C3a), 106.6 (C5′), 113.9 (C3), 114.2–
131.9 (Carom), 142.7 (C6′), 143.0 (Carom), 143.4 (Carom),
150.0 (C2), 161.4 (C4), 162.5 (C1), 162.9 (Carom), 188.4
(3-C=O). Found, %: C 67.27; H 4.76; N 3.15.
C25H21NO7. Calculated, %: C 67.11; H 4.73; N 3.13.
H
arom), 9.34 br.s (1H, OH). 13C NMR spectrum
(100 MHz, CDCl3), δC, ppm: 27.6 (C3′), 64.3 (C2′),
71.0 (C3a), 107.99 (C4′), 114.8 (C3), 116.9–135.4
(Carom), 143.3 (C6′), 143.9 (Carom), 148.2 (C2), 161.1
(C4), 164.3 (C1), 188.6 (3-C=O). Found, %: C 56.58;
H 2.93; N 2.87. C22H14BrNO6. Calculated, %: C 56.43;
H 3.01; N 2.99.
3-Benzoyl-3a-(3,4-dihydro-2H-pyran-5-yl)-
2-hydroxypyrrolo[2,1-c][1,4]benzoxazine-1,4(3aH)-
dione (3e). Yield 0.78 g (62%), mp 120–122°C
(decomp., from isooctane). IR spectrum, ν, cm–1: 3200
(O–H), 1776 (C4=O), 1715 (C1=O), 1654 (3-C=O).
1H NMR spectrum (400 MHz, DMSO-d6), δ, ppm:
1.60 m (2H, 3′-H), 1.80 m (2H, 4′-H), 3.70 m and
3.87 m (1H each, 2′-H), 6.26 s (1H, 6′-H), 7.33–7.90 m
(9H, Harom), 11.76 br.s (1H, OH). 13C NMR spectrum
(126 MHz, DMSO-d6), δC, ppm: 17.1 (C4′), 20.9 (C3′),
65.1 (C2′), 67.4 (C3a), 106.5 (C5′), 113.1 (C3), 116.5–
137.7 (Carom), 142.8 (C6′), 143.4 (Carom), 150.9 (C2),
161.4 (C4), 162.8 (C1), 190.0 (3-C=O). Found, %:
C 68.32; H 4.35; N 3.26. C23H17NO6. Calculated, %:
C 68.48; H 4.25; N 3.47.
3-(4-Bromobenzoyl)-3a-(3,4-dihydro-2H-pyran-
5-yl)-2-hydroxypyrrolo[2,1-c][1,4]benzoxazine-
1,4(3aH)-dione (3i). Yield 0.79 g (53%), mp 170–
172°C (decomp., from toluene). IR spectrum, ν, cm–1:
3087 (O–H), 1778 (C4=O), 1703 (C1=O), 1650
(3-C=O). 1H NMR spectrum (500 MHz, DMSO-d6), δ,
ppm: 1.59 m (2H, 3′-H), 1.79 m (2H, 4′-H), 3.70 m and
3.87 m (1H each, 5′-H), 6.27 s (1H, 6′-H), 7.34–7.84 m
(8H, Harom), 11.93 br.s (1H, OH). 13C NMR spectrum
(126 MHz, DMSO-d6), δC, ppm: 17.1 (C4′), 20.9 (C3′),
65.2 (C2′), 67.4 (C3a), 106.4 (C5′), 114.3 (C3), 116.5–
136.7 (Carom), 142.9 (C6′), 143.4 (Carom), 151.0 (C2),
161.4 (C4), 162.7 (C1), 189.2 (3-C=O). Found, %:
C 57.36; H 3.53; N 2.78. C23H16BrNO6. Calculated, %:
C 57.28; H 3.34; N 2.90.
3-Benzoyl-8-chloro-3a-(3,4-dihydro-2H-pyran-
5-yl)-2-hydroxypyrrolo[2,1-c][1,4]benzoxazine-
1,4(3aH)-dione (3f). Yield 0.91 g (66%), mp 235–
237°C (decomp., from isooctane). IR spectrum, ν,
cm–1: 3175 (O–H), 1770 (C4=O), 1727 (C1=O), 1664
(3-C=O). 1H NMR spectrum (400 MHz, DMSO-d6), δ,
ppm: 1.64 m (2H, 3′-H), 1.80 m (2H, 4′-H), 3.74 m and
3.89 m (1H each, 5′-H), 6.27 s (1H, 6′-H), 7.40–7.90 m
(8H, Harom), 11.84 br.s (1H, OH). Found, %: C 63.24;
H 3.47; N 3.53. C23H16ClNO6. Calculated, %: C 63.09;
H 3.68; N 3.20.
The X-ray diffraction data for compound 3i were
obtained from a 0.31×0.25×0.10-mm colorless single
crystal on an Xcalibur S automated diffractometer
according to standard procedure [MoK radiation,
graphite monochromator, ω-scanning with a step of 1°,
295(2) K]. The structure was solved and refined using
SHELXTL software package [24] in anisotropic
approximation for non-hydrogen atoms (isotropic for
hydrogens). Cubic crystal system, space group Ia–3d;
unit cell parameters: a = 37.8244(14) Å; V =
54115(3) Å3; Z = 96; d = 1.421 g/cm3; μ = 1.861 mm–1.
Total of 21787 reflection intensities were measured in
the range 2.75 < θ < 26.40°, including 4541 indepen-
3a-(3,4-Dihydro-2H-pyran-5-yl)-2-hydroxy-3-
(4-methoxybenzoyl)pyrrolo[2,1-c][1,4]benzoxazin-
1,4(3aH)-dione (3g). Yield 0.83 g (61%), mp 104–
105°C (decomp., from isooctane). IR spectrum, ν,
cm–1: 3187 (O–H), 1776 (C4=O), 1715 (C1=O), 1651
(3-C=O). 1H NMR spectrum (500 MHz, DMSO-d6), δ,
ppm: 1.59 m (2H, 3′-H), 1.80 m (2H, 4′-H), 3.69 m
(1H, 5′-H), 3.86 m (4H, MeO, 5′-H), 6.23 s (1H, 6′-H),
7.02–7.88 m (8H, Harom), 11.56 br.s (1H, OH).
13C NMR spectrum (126 MHz, DMSO-d6), δC, ppm:
17.0 (C4′), 20.9 (C3′), 55.5 (Me), 65.1 (C2′), 67.5 (C3a),
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TWO CONCURRENT PATHWAYS OF THE REACTION OF PYRROLOBENZOXAZINE...
79
dent reflections (Rint = 0.0888) and 1394 reflections
with Ι > 2σ(I); completeness 97.9%. A correction for
absorption was applied analytically. Final divergence
factors: R1 = 0.0601, wR2 = 0.1064 [for reflections with
Ι > 2σ(I)], R1 = 0.2428, wR2 = 0.1244 (all reflections);
goodness of fit 1.004, Δρ = 0.398/–0.419 ēÅ–3. The
crystallographic data for compound 3i were deposited
to the Cambridge Crystallographic Data Centre
(CCDC entry no. 1519733).
(2S*,1R*,6R*)-8-(4-Ethoxyphenyl)-5,7,19-trioxa-
12-azapentacyclo[10.8.0.01,9.02,6.013,18]icosa-
8,13,15,17-tetraene-10,11,20-trione (4c). Yield 0.47 g
(35%), mp 274–275°C (decomp., from benzene). IR
spectrum, ν, cm–1: 1766 (C20=O), 1741 (C10=O), 1710
1
(C11=O). H NMR spectrum (400 MHz, CDCl3), δ,
ppm: 1.47 t (3H, Me, J = 7.0 Hz), 1.67–1.77 m and
1.84–1.93 m (1H each, 3-H), 3.03 t.d (1H, 2-H, J =
9.5, 5.5 Hz), 4.06 q (1H, 4-H, J = 8.0 Hz), 4.11–4.23 m
(3H, 4-H, OCH2Me), 6.02 d (1H, 6-H, J = 5.3 Hz),
6.99–8.11 m (8H, Harom). 13C NMR spectrum
(100 MHz, CDCl3), δC, ppm: 14.1 (Me), 22.8 (C3),
43.2 (C2), 59.0 (C1), 63.5 (CH2Me), 68.6 (C4), 96.7
(C6), 103.1 (C9), 113.6–142.8 (Carom), 159.8 (C11),
162.8 (C20), 163.9 (Carom), 169.8 (C8), 174.0 (C10).
Found, %: C 66.40; H 4.46; N 3.37. C24H19NO7. Cal-
culated, %: C 66.51; H 4.42; N 3.23.
3a-(3,4-Dihydro-2H-pyran-5-yl)-2-hydroxy-
3-(4-nitrobenzoyl)pyrrolo[2,1-c][1,4]benzoxazine-
1,4(3aH)-dione (3j). Yield 0.78 g (59%), mp 198–
200°C (decomp., from isooctane). IR spectrum, ν,
cm–1: 3182 (O–H), 1785 (C4=O), 1710 (C1=O), 1650
(3-C=O). 1H NMR spectrum (400 MHz, DMSO-d6), δ,
ppm: 1.57 m (2H, 3′-H), 1.75 m (2H, 4′-H), 3.69 m and
3.84 m (1H each, 5′-H), 6.30 s (1H, 6′-H), 7.34–8.31 m
(8H, Harom), 11.76 br.s (1H, OH). Found, %: C 61.35;
H 3.66; N 6.51. C23H16N2O8. Calculated, %: C 61.61;
H 3.60; N 6.25.
(2S*,1R*,6R*)-8-(Bromophenyl)-5,7,19-trioxa-
12-azapentacyclo[10.8.0.01,9.02,6.013,18]icosa-
8,13,15,17-tetraene-10,11,20-trione (4d). Yield 0.43 g
(30%), mp 280–281°C (decomp., from benzene).
IR spectrum, ν, cm–1: 1779 (C20=O), 1739 (C10=O,
(2S*,1R*,6R*)-8-Phenyl-5,7,19-trioxa-12-aza-
pentacyclo[10.8.0.01,9.02,6.013,18]icosa-8,13,15,17-
tetraene-10,11,20-trione (4a). Yield 0.34 g (28%),
mp 271–272°C (decomp., from benzene). IR spectrum,
ν, cm–1: 1779 (C20=O), 1728 (C10=O, C11=O). 1H NMR
spectrum (400 MHz, DMSO-d6), δ, ppm: 1.57–1.67 m
and 1.77–1.85 m (1H each, 3-H), 3.22 m (1H, 2-H),
3.97 q (1H, 4-H, J = 7.9 Hz), 4.13 t.d (1H, 4-H, J =
9.0, 4.0 Hz), 6.00 d (1H, 6-H, J = 5.3 Hz), 7.36–7.87 m
(9H, Harom). 13C NMR spectrum (100 MHz,
DMSO-d6), δC, ppm: 22.8 (C3), 42.2 (C2), 58.8 (C1),
68.9 (C4), 99.4 (C6), 104.1 (C9), 116.9–143.1 (Carom),
159.9 (C11), 163.1 (C20), 167.0 (C8), 176.1 (C10).
Found, %: C 67.99; H 4.01; N 3.66. C22H15NO6. Cal-
culated, %: C 67.86; H 3.88; N 3.60.
1
C11=O). H NMR spectrum (400 MHz, CDCl3), δ,
ppm: 1.67–1.77 m and 1.87–1.96 m (1H each, 3-H),
3.02 t.d (1H, 2-H, J = 9.7, 5.1 Hz), 4.08 q (1H, 4-H,
J = 8.0 Hz), 4.19 t.d (1H, 4-H, J = 9.2, 4.4 Hz), 6.04 d
(1H, 6-H, J = 5.3 Hz), 7.30–7.95 m (8H, Harom). Found,
%: C 56.50; H 3.11; N 3.12. C22H14BrNO6. Calculated,
%: C 56.43; H 3.01; N 2.99.
(2S*,1R*,7R*)-9-Phenyl-6,8,20-trioxa-13-aza-
pentacyclo[11.8.0.01,10.02,7.014,19]henicosa-9,14,16,18-
tetraene-11,12,21-trione (4e). Yield 0.40 g (32%),
mp 299–300°C (decomp., from benzene). IR spectrum,
ν, cm–1: 1778 (C21=O), 1727 (C11=O, C12=O). 1H NMR
spectrum (400 MHz, DMSO-d6), δ, ppm: 1.10–1.27 m
and 1.43 m (1H each, 3-H), 1.48–1.68 m (2H, 4-H),
2.44 m (1H, 2-H), 3.80 m (2H, 5-H), 5.74 m (1H, 7-H),
7.38–7.89 m (9H, Harom). 13C NMR spectrum
(126 MHz, DMSO-d6), δC, ppm: 17.7 (C3), 22.2 (C4),
32.6 (C2), 60.7 (C1), 61.0 (C5), 97.2 (C7), 99.0 (C10),
117.0–143.5 (Carom), 160.2 (C12), 163.4 (C21), 167.0
(C9), 176.1 (C11). Found, %: C 68.50; H 4.22; N 3.73.
C23H17NO6. Calculated, %: C 68.48; H 4.25; N 3.47.
(2S*,1R*,6R*)-15-Chloro-8-phenyl-5,7,19-trioxa-
12-azapentacyclo[10.8.0.01,9.02,6.013,18]icosa-
8,13,15,17-tetraene-10,11,20-trione (4b). Yield 0.41 g
(31%), mp 278–280°C (decomp., from benzene). IR
spectrum, ν, cm–1: 1773 (C20=O), 1738 (C10=O), 1713
1
(C11=O). H NMR spectrum (400 MHz, CDCl3), δ,
ppm: 1.68–1.78 m and 1.91–2.00 m (1H each, 3-H),
3.02 t.d (1H, 2-H, J = 9.5, 5.3 Hz), 4.12 q (1H, 4-H,
J = 8.0 Hz), 4.13 t.d (1H, 4-H, J = 9.2, 4.6 Hz), 6.05 d
(1H, 6-H, J = 5.3 Hz), 7.24–8.04 m (8H, Harom).
13C NMR spectrum (100 MHz, CDCl3), δC, ppm: 23.2
(C3), 43.6 (C2), 59.3 (C1), 69.3 (C4), 98.1 (C6), 104.0
(C9), 118.3–141.8 (Carom), 159.2 (C11), 162.0 (C20),
170.4 (C8), 173.9 (C10). Found, %: C 62.48; H 3.41;
N 3.22. C22H14ClNO6. Calculated, %: C 62.35;
H 3.33; N 3.31.
(2S*,1R*,7R*)-16-Chloro-9-phenyl-6,8,20-trioxa-
13-azapentacyclo[11.8.0.01,10.02,7.014,19]henicosa-
9,14,16,18-tetraene-11,12,21-trione (4f). Yield 0.33 g
(24%), mp 269–270°C (decomp., from benzene).
IR spectrum, ν, cm–1: 1785 (C21=O), 1736 (C11=O,
1
C12=O). H NMR spectrum (500 MHz, DMSO-d6), δ,
ppm: 1.07–1.16 m and 1.50 m (1H each, 3-H), 1.55–
1.66 m (2H, 4-H), 2.54 m (1H, 2-H), 3.80 m (2H, 5-H),
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STEPANOVA et al.
80
5.73 d (1H, 7-H, J = 3.9 Hz), 7.42–7.90 m (8H, Harom).
13C NMR spectrum (126 MHz, DMSO-d6), δC, ppm:
17.6 (C3), 22.2 (C4), 32.5 (C2), 60.6 (C1), 61.0 (C5),
97.2 (C7), 98.8 (C10), 118.7–142.3 (Carom), 160.1 (C12),
162.9 (C21), 167.3 (C9), 175.6 (C11). Found, %:
C 63.40; H 3.28; N 3.33. C23H16ClNO6. Calculated, %:
C 63.09; H 3.68; N 3.20.
Found, %: C 66.42; H 4.28; N 3.37. C24H19NO7. Cal-
culated, %: C 66.51; H 4.42; N 3.23.
(2S*,1R*,7R*)-9-(4-Ethoxyphenyl)-6,8,20-trioxa-
13-azapentacyclo[11.8.0.01,10.02,7.014,19]henicosa-
9,14,16,18-tetraene-11,12,21-trione (4h). Yield 0.37 g
(27%), mp 269–270°C (decomp., from benzene). IR
spectrum, ν, cm–1: 1778 (C21=O), 1731 (C11=O,
1
C12=O). H NMR spectrum (400 MHz, DMSO-d6), δ,
X-Ray analysis of compound 4f. A single crystal
of 4f (yellow plate) for X-ray analysis was obtained by
crystallization from toluene. The X-ray diffraction data
were acquired on an Xcalibur R automated four-circle
diffractometer with χ-geometry (monochromatized
MoKa radiation, ω-scanning) using CrysAlisPro soft-
ware [21]. Triclinic crystal system, space group P-1;
C23H16ClNO6; unit cell parameters: a = 9.2253(13), b =
10.7101(13), c = 11.3059(15) Å; α = 73.195(11), β =
81.299(11), γ = 69.205(12)°; V = 998.2(2) Å3; M =
437.82; dcalc = 1.457 g/cm3; Z = 2. Total of 7726 re-
flection intensities were collected in the range 2.94 <
θ < 29.40°, including 4592 independent reflections
(Rint = 0.0450) and 3403 reflections with I > 2σ(I);
completeness 99.6% for θ < 26°. Absorption by the
crystal was taken into account using SCALE3
ABSPACK algorithm [25]. The structure was solved
and refined using SHELX97 [24]. The positions of all
non-hydrogen atoms were refined independently in
anisotropic approximation; hydrogen atoms were
placed in geometrically calculated positions and
refined according to the riding model with dependent
thermal parameters. Final divergence factors: R1 =
0.0649, wR2 = 0.1648 [reflections with I > 2σ(I)]; R1 =
0.0866, wR2 = 0.1828 (all reflections); goodness of fit
S = 1.068; Δ ρ = 0.362/–0.563 ēÅ–3. The crystallo-
graphic data for compound 4f were deposited to the
Cambridge Crystallographic Data Centre (CCDC entry
no. 1519734).
ppm: 1.04–1.15 m (1H, 3-H), 1.38 t (3H, Me, J =
6.9 Hz), 1.42 m (1H, 3-H), 1.49–1.63 m (2H, 4-H),
3
2.44 d.t (1H, 2-H, 2J = 12.8, J = 4.4 Hz), 3.70–3.81 m
(2H, 5-H), 4.17 d.q (2H, CH2Me, J = 6.9, 2.0 Hz),
5.71 d (1H, 7-H, J = 3.7 Hz), 7.11–7.92 m (8H, Harom).
13C NMR spectrum (126 MHz, DMSO-d6), δC, ppm:
14.5 (Me), 17.6 (C3), 22.1 (C4), 32.8 (C2), 60.8 (C1),
60.8 (C5), 63.6 (CH2Me), 96.9 (C7), 97.8 (C10), 113.7–
143.4 (Carom), 160.4 (C12), 162.6 (Carom), 163.4 (C21),
167.0 (C9), 175.5 (C11). Found, %: C 67.30; H 4.68;
N 3.31. C25H21NO7. Calculated, %: C 67.11; H 4.73;
N 3.13.
(2S*,1R*,7R*)-9-(4-Bromophenyl)-6,8,20-trioxa-
13-azapentacyclo[11.8.0.01,10.02,7.014,19]henicosa-
9,14,16,18-tetraene-11,12,21-trione (4i). Yield 0.25 g
(17%), mp 270–271°C (decomp., from benzene). IR
spectrum, ν, cm–1: 1782 (C21=O), 1738 (C11=O,
1
C12=O). H NMR spectrum (500 MHz, DMSO-d6), δ,
ppm: 1.11–1.23 m and 1.42 m (1H each, 3-H), 1.49–
1.63 m (2H, 4-H), 2.48 m (1H, 2-H), 3.74–3.82 m (2H,
5-H), 5.74 d (1H, 7-H, J = 3.7 Hz), 7.38–7.82 m (8H,
Harom). 13C NMR spectrum (126 MHz, DMSO-d6), δC,
ppm: 17.6 (C3), 22.2 (C4), 32.6 (C2), 60.7 (C1), 61.0
(C5), 97.4 (C7), 99.4 (C10), 117.0–143.4 (Carom), 160.0
(C12), 163.2 (C21), 165.7 (C9), 176.1 (C11). Found, %:
C 57.43; H 3.23; N 2.63. C23H16BrNO6. Calculated, %:
C 57.28; H 3.34; N 2.90.
(2S*,1R*,7R*)-9-(4-Nitrophenyl)-6,8,20-trioxa-
13-azapentacyclo[11.8.0.01,10.02,7.014,19]henicosa-
9,14,16,18-tetraene-11,12,21-trione (4j). Yield 0.25 g
(19%), mp 265–266°C (decomp., from benzene). IR
spectrum, ν, cm–1: 1793 (C21=O), 1732 (C11=O,
(2S*,1R*,7R*)-9-(4-Methoxyphenyl)-6,8,20-tri-
oxa-13-azapentacyclo[11.8.0.01,10.02,7.014,19]henicosa-
9,14,16,18-tetraene-11,12,21-trione (4g). Yield 0.34 g
(25%), mp 272–374°C (decomp., from benzene). IR
spectrum, ν, cm–1: 1780 (C21=O), 1737 (C11=O,
1
C12=O). H NMR spectrum (400 MHz, DMSO-d6), δ,
ppm: 1.20–1.28 m and 1.43 m (1H each, 3-H), 1.52–
1.66 m (2H, 4-H), 2.55 m (1H, 2-H), 3.81 m (2H, 5-H),
5.79 d (1H, 7-H, J = 3.5 Hz), 7.37–8.43 m (8H, Harom).
Found, %: C 61.89; H 3.48; N 6.38. C23H16N2O8. Cal-
culated, %: C 61.61; H 3.60; N 6.25.
This study was performed under financial support
by the Ministry of Education and Science of the
Russian Federation (project no. 965) and by the
Russian Foundation for Basic Research (project
nos. 16-43-590613, 14-03-96005).
1
C12=O). H NMR spectrum (500 MHz, DMSO-d6), δ,
ppm: 1.06–1.13 m and 1.42 m (1H each, 3-H), 1.50–
1.62 m (2H, 4-H), 2.44 d.t (1H, 2-H, J = 12.5, 4.0 Hz),
3.77 m (2H, 5-H), 3.89 s (3H, Me), 5.71 d (1H, 7-H,
J = 4.0 Hz), 7.12–7.94 m (8H, Harom). 13C NMR spec-
trum (126 MHz, DMSO-d6), δC, ppm: 17.6 (C3), 22.1
(C4), 32.8 (C2), 55.6 (Me), 60.8 (C1), 60.9 (C5), 96.9
(C7), 97.9 (C10), 113.4–143.4 (Carom), 160.4 (C12),
163.3 (Carom), 163.4 (C21), 167.0 (C9), 175.5 (C11).
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TWO CONCURRENT PATHWAYS OF THE REACTION OF PYRROLOBENZOXAZINE...
81
13. Stepanova, E.E. and Maslivets, A.N., Russ. J. Org.
Chem., 2015, vol. 51, p. 1052.
REFERENCES
1. Nicolaou, K.C., Snyder, S.A., Montagnon, T., and
Vassilikogiannakis, G., Angew. Chem., Int. Ed., 2002,
vol. 41, p. 1668.
2. Jørgensen, K.A., Eur. J. Org. Chem., 2004, p. 2093.
3. Eschenbrenner-Lux, V., Kumar, K., and Waldmann, H.,
Angew. Chem., Int. Ed., 2014, vol. 53, no. 42, p. 11146.
4. Tsuda, Y., Horiguchi, Y., and Sano, T., Heterocycles,
1976, vol. 4, p. 1237.
5. Sano, T., J. Synth. Org. Chem., 1984, vol. 42, p. 340.
14. Stepanova, E.E. and Maslivets, A.N., Russ. J. Org.
Chem., 2016, vol. 52, p. 879.
15. Babenysheva, A.V. and Maslivets, A.N., Russ. J. Org.
Chem., 2008, vol. 44, p. 774.
16. Mayr, H. and Patz, M., Angew. Chem., Int. Ed. Engl.,
1994, vol. 33, p. 938.
17. Evans, D.A., Johnson, J.S., and Olhava, E.J., J. Am.
Chem. Soc., 2000, vol. 122, p. 1635.
18. Stepanova, E.E. and Maslivets, A.N., Russ. J. Org.
Chem., 2015, vol. 51, p. 1050.
6. Horiguchi, Y., Sano, T., and Tsuda, Y., Chem. Pharm.
Bull., 1996, vol. 44, p. 670.
7. Dmitriev, M.V., Silaichev, P.S., and Maslivets, A.N.,
19. Stepanova, E.E. and Maslivets, A.N., Russ. J. Org.
Chem., 2014, vol. 50, p. 1382.
Russ. J. Org. Chem., 2009, vol. 45, p. 1873.
20. Amagata, T., Doi, M., Tohgo, M., Minoura, K., and
8. Silaichev, P.S., Kudrevatykh, N.V., Aliev, Z.G., and
Maslivets, A.N., Russ. J. Org. Chem., 2012, vol. 48,
p. 253.
Numata, A., Chem. Commun., 1999, p. 1321.
21. Wildman, W.C. and Bailey, D.T., J. Org. Chem., 1968,
vol. 33, p. 3749.
9. Silaichev, P.S., Kudrevatykh, N.V., and Maslivets, A.N.,
22. Chawla, A.S., Jackson, A.H., Ludgate, P., J. Chem. Soc.,
Perkin Trans. 1, 1982, p. 2903.
Russ. J. Org. Chem., 2012, vol. 48, p. 1103.
10. Bubnov, N.V., Stepanova, E.E., Dmitriev, M.V., and
Maslivets, A.N., Russ. J. Org. Chem., 2015, vol. 51,
p. 1404.
23. Aguilar, M.I., Giral, F., and Espejo, O., Phytochemistry,
1981, vol. 20, p. 2061.
24. Sheldrick, G.M., Acta Crystallogr., Sect. A, 2008,
11. Silaichev, P.S., Kryuchkova, M.A., and Maslivets, A.N.,
vol. 64, p. 112.
Russ. J. Org. Chem., 2010, vol. 46, p. 607.
25. CrysAlisPro, Agilent Technologies, Version 1.171.37.33
(release 27-03-2014 CrysAlis171.NET).
12. Stepanova, E.E., Aliev, Z.G., and Maslivets, A.N., Russ.
J. Org. Chem., 2013, vol. 49, p. 1762.
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